Delayed reaction automatic kinescope biasing system

Abstract

An automatic kinescope bias (AKB) control system for a television receiver operates in response to an enabling timing signal for maintaining a desired level of kinescope blanking current. The timing signal is applied to a control input of the AKB system via a timing signal coupling path. The timing signal input to the AKB system is inhibited for a given time interval after the receiver is initially energized, to delay AKB action until the kinescope has reached a desired operating temperature. The timing signal is inhibited by means of a control network coupled to the timing signal path. The given time interval is determined by a time constant circuit which is associated with the control network and which is substantially insensitive to the amplitude, and duty cycle of the timing signal.

What is claimed is: 
     
       1. In a video signal processing system including a kinescope for displaying an image in response to image representative video signals applied thereto said kinescope exhibiting an initial conduction characteristic during an initial interval commencing when said system is initially energized, and exhibiting a normal conduction characteristic afterwards; means for supplying system operating voltages when said system is energized; and bias control means coupled to said kinescope and operative in response to a timing signal supplied thereto via a timing signal coupling path, for automatically controlling the bias of said kinescope; apparatus comprising: timing control means for inhibiting said timing signal during said initial interval so that said bias control means is rendered inoperative for the duration of said initial interval, said timing control means comprising a time constant network coupled to said operating voltage supplying means; and   a threshold conduction network with an input coupled to said time constant network and an output coupled to said timing signal path, said threshold network exhibiting first and second conductive states in response to bias provided from said time constant network substantially independent of the amplitude and duty cycle of said timing signal; wherein said threshold network exhibits (a) said first conductive state during said timing signal in said signal path, and (b) said second conductive state at the end of said initial interval for then enabling said timing signal in said signal path.     
     
     
       2. Apparatus according to claim 1, wherein said system comprises a television receiver for processing video signals comprising image display and image blanking intervals;   said timing signal is in synchronism with vertical image blanking intervals of said video signal; and   said control means operates in response to said timing signals during said vertical blanking intervals for maintaining a desired level of kinescope blanking current; and   said threshold network maintains a substantially fixed potential on said timing signal path, to the exclusion of said timing signal, during said initial interval.   
     
     
       3. Apparatus according to claim 1, wherein said threshold conduction network comprises an active current conducting device with an input electrode, and output and common electrodes defining a main current conduction path of said active device between said timing signal path and a reference potential; and   said time constant network is coupled to said input of said active device.   
     
     
       4. Apparatus according to claim 3, wherein said active device corresponds to a transistor with a base input electrode coupled to said time constant network, a collector output electrode coupled to said timing signal path, and a common emitter electrode coupled to a reference potential.   
     
     
       5. Apparatus according to claim 4, wherein said time constant network comprises a resistor and a capacitor coupled in series between a source of DC voltage and said base input of said transistor.   
     
     
       6. Apparatus according to claim 5, and further comprising an impedance DC coupled from said base electrode of said transistor to a reference potential.   
     
     
       7. Apparatus according to claim 4, wherein said transistor exhibits a saturated conductive state during said initial interval.   
     
     
       8. In a color television receiver for processing color image representative video signals having image display and blanking intervals, said receiver including an image reproducing kinescope with plural intensity control electron guns each having associated cathode and grid electrodes, said kinescope exhibiting an initial conduction characteristic during an initial interval commencing when said receiver is initially energized, and exhibiting a normal conduction characteristic afterwards; means for supplying receiver operating voltages when said receiver is energized; plural bias control means respectively coupled to said kinescope electron guns and operative in response to a timing signal supplied thereto for automatically controlling the bias of said kinescope; and means for supplying a timing signal in common to said plural control means via a timing signal coupling path; apparatus comprising: timing control means for inhibiting said timing signal during said initial interval so that said plural bias control means are rendered inoperative for the duration of said initial interval, said timing control means comprising a time constant network coupled to said operating voltage supplying means; and   a threshold conduction network with an input coupled to said time constant network and an output coupled to said timing signal path, said threshold network exhibiting first and second conductive states in response to bias provided from said time constant network substantially independent of the amplitude and duty cycle of said timing signal; wherein said threshold network exhibits (a) said first conductive state during said initial interval for then inhibiting said timing signal in said signal path, and (b) said second conductive state at the end of said initial interval for then enabling said timing signal in said signal path.